Unmanned underwater vehicles (UUVs) are used for various underwater exploration applications, including inspection of underwater structures (oil and gas platforms, etc.), mine neutralization, etc. As a result, it may be desirable that such UUVs be of relatively low cost, i.e., expendable. To keep the cost of UUVs low, precision underwater navigation components are typically not carried by the UUV.
One approach to guiding a low cost or expendable UUV is by a fiber-optic communications link connected between a host control ship and the UUV. Yet, in applications such as those noted above, it may be desirable for the host ship to deploy the UUV from a long stand-off distance, rather than deposit the UUV in close proximity to the area of interest. However, long stand-off distances require a relatively precise guidance and navigation capability to maneuver the UUV into a range where terminal homing sensors, such as video cameras, or a closed-loop guidance system may be used to guide the vehicle, for example.
Ultra-short baseline (USBL) is one technique that is used for underwater acoustic positioning. A conventional USBL system typically includes a transceiver, which is mounted under a ship, and a transponder/responder on the, seafloor, a towfish, or on a UUV. A computer, or “topside unit,” is used to calculate a position from the ranges and bearings measured by the transceiver.
U.S. Pat. No. 6,854,410 is directed to an unmanned system for investigating underwater regions which utilizes an unmanned mothership and a plurality of UUVs. The mothership transports the UUVs to and from the vicinity of an underwater region, releases the UUVs into the water, and facilitates recovery of the UUVs from the water. Each UUV can traverse an underwater region, generate sonar and image data associated with the underwater region, and transmit the sonar and image data through the water for receipt and re-transmission by the mothership. A docking system mounted partially onboard the mothership and partially onboard each UUV couples each UUV to the mothership and selectively releases each UUV into the underwater region. A guidance system mounted partially onboard the mothership and partially onboard each UUV guides each UUV back to the docking system from positions in the water. The mothership and UUVs can also be equipped with a non-contact electrical energy transfer system so that each UUV can return to the mothership and re-charge onboard batteries while underwater.
Despite the advantages of such systems, further enhancements to UUV guidance and navigation systems may be desirable in certain applications.